Woods and wood composites such as solid wood and glued laminated lumber and the like have conventionally been used primarily as framing structures such as column and beam in buildings, and additionally in recent years, attention has been focused on the attempts to apply such solid wood and glued laminated lumber to large scale constructions such as wood bridge and large-scale dome. Among such solid wood and glued laminated lumber, the glued laminated lumber is produced by arranging the fiber directions of sweeping laminae or small square timbers preliminarily cut in longer lengths in parallel along the fiber directions and thereafter laminating them together vertically or arranging them horizontally to bond them together with adhesives, and compared with solid wood, therefore, the glued laminated lumber has characteristic properties such as higher freedom from dimension and shape and less dispersion in product strength and less occurrence of crack and warp during drying, so such glued laminated lumber has good advantages such as ready production of curved materials.
So as to impart sufficient rigidity and strength to woods such as solid wood and glued laminated lumber if used for large-scale buildings and constructions, however, it is required to enlarge the thickness thereof, so that the ceiling of the buildings and constructions is essentially low, or is high more than necessary, disadvantageously.
As a wood material with enhanced rigidity and strength but with no enlarged thickness, it has been proposed recently carbon fiber reinforced wood and carbon fiber reinforced glued laminated lumber, which are produced by bonding carbon fiber through adhesives to single wood or glued laminated lumber.
For example, Japanese Patent Laid-open No. Hei 3-230904 discloses a process comprising arranging carbon fiber on the surface of wood coated with an adhesive, thereby impregnating the adhesive into the fiber and bonding the wood together. Additionally, for example, Japanese Patent Laid-open No. Sho 53-108182 discloses a process comprising preliminarily impregnating carbon fiber with an adhesive to prepare a carbon fiber prepreg, which is then bonded to wood to reinforce the wood.
In so-called composite materials reinforced with carbon fiber, epoxy resins are frequently used as the matrix resins. Epoxy resins have a drawback of extremely poor thermal resistance or fire resistance although the resins have extremely great adhesivity to carbon fiber. Hence, wood reinforced with composite materials produced by using epoxy resins cannot satisfy the provision of thermal resistance or fire resistance required for large scale buildings or large scale constructions.
So as to reinforce wood or glued laminated lumbers in recent years, attempts have been made to reinforce wood or glued laminated lumbers with composite materials comprising carbon fiber and matrix resins. As the adhesive material (matrix resin) to be used for such composite materials, resins such as phenol based resins and resorcin based resins are used.
These resins are said to have sufficient water resistance, corrosion resistance, fire resistance and thermal resistance required for wood buildings and constructions and to be effective for adhesion between woods.
When these matrix resins are used to prepare a carbon fiber prepreg, however, there have been the following problems; a problem of poor adhesivity between carbon fiber and the matrix resins; a problem of poor adhesivity between carbon fiber and wood; a problem of poor fluidity of the matrix resins during the adhesion to wood; and a problem of extreme difficulty in preparing a prepreg with a longer shelf life having a longer usable time, which is inevitable for plant production under controls.
Furthermore, conventional carbon fiber prepreg is poor in adhesivity to wood such as wood and glued laminated lumber and therefore, the resulting carbon fiber reinforced wood and carbon fiber reinforced glued laminated lumber have low rigidity and strength in spite of the amount of the carbon fiber used therein, so expensive carbon fiber should be used at a greater amount than necessary and carbon fiber is hence not efficiently used.
When conventional carbon fiber prepreg is bonded to wood such as wood and glued laminated lumber, additionally, the bonded layer is disadvantageously peeled off during use. As one of the causes, it has been inferred that the matrix resins might have a close relation.
When intending the adhesion of a carbon fiber prepreg to wood, the adhesivity varies because wood is a natural product having variable properties, depending on the wood species and their growing environment and others. So as to procure adhesivity, furthermore, laborious adjustments are needed, including the selection and adjustment of the state of the matrix resins to be used for such prepreg, namely solid, semi solid or liquid state thereof, as well as the amount thereof, so economical and quality problems have been present.
So as to roll a carbon fiber prepreg in a roll or stack the prepreg in sheet for delivery or storage, furthermore, release paper is arranged on one face or both the faces of the prepreg so as to avoid the adhesion of each other, but laborious and time consuming processing works such as the removal of the release paper when the prepreg is attached to wood are necessary, problematically and the removed release paper turns waste to cause environmental pollution.
So as to overcome these conventional problems, the present inventors have made investigations and consequently, the inventors have found that these problems can be overcome by preparing a carbon fiber prepreg by using a mixture resin containing a specific matrix resin and a specific curing agent and a specific curing catalyst, and have attained the present invention. Additionally, the inventors have found that these problems can be overcome by a specific carbon fiber sheet and a carbon fiber reinforced wood, and have attained the present invention.
In other words, it is the object of a first group of the present invention to provide a carbon fiber prepreg having excellent adhesivity and a longer usable time such that the prepreg can be bonded to wood or glued laminated lumbers for use and which can impart the elasticity modulus and strength of the carbon fiber to wood and glued laminated lumbers at a higher ratio. It is the other object in association with the first group of the present invention to provide wood, a glued laminated lumber and a wood laminated material having high rigidity and strength, herein the carbon fiber prepreg is used.
It is the object of a second group of the present invention to provide a carbon fiber prepreg attached wood based sheet , and a carbon fiber composite wood based sheet produced by curing the sheet, in which carbon fiber prepreg is a carbon fiber sheet or a carbon fiber strand prepreg with excellent adhesivity, handleability and processability and with no occurrence of environmental pollution, which sheet can be bonded to wood and glued laminated lumbers for use. It is the other object in association with the second group of the present invention to provide wood or a glued laminated lumber with high rigidity and strength, where the carbon fiber prepreg attached wood based sheet and a carbon fiber composite wood based sheet produced by curing the sheet are used.
Other objects in association with the first group of the present invention and the second group of the present invention enlarge the utility of wood to large scale buildings and constructions, which is never conventionally possible, and are to provide wood and a glued laminated lumber as reinforced with carbon fiber, which are useful for reducing the amount of natural wood to be used and reducing the weight of the resulting buildings and constructions.